The gecko visual pigments with their unusual and useful properties will continue to be investigated especially with respect to the effects of varying the pH and other reagents, like the -SH poisons, that are known to affect the protein structure. An attempt will be made to discover the nature of the changes in protein structure thought to occur in response to the physical and chemical treatments that are known to influence the color of the pigment. These changes are of social interest for they are all reversible, so that they have physiological implications. In these attempts one technique that will be employed is the measurement of circular dichroism in the visible and ultraviolet spectral regions and the changes in circular dichroism evoked by the above-mentioned treatments. Snakes will be employed, whose visual cells are known, to search out the possibilities of extracting cone pigments or those pigments associated with so-called transmuted visual cells. Finally, the gecko receptor potential recorded from the isolated, perfused retina will be examined in the light of the knowledge now available on the bahavior of the photopigment under various treatments.